Chapter 1

SIGNAL PROCESSING:  Signal processing is concerned with the efficient and accurate extraction of information in a signal process.  Signal processing provides the methods and tools for the extraction of information from signals.  The application of signal processing involves TV, radio, cellular mobile phones, radar, sonar etc.

SIGNAL :  A signal is a means of conveying information. Examples  Imaging radars calculate the round trip delay of reflected light bouncing from the surface of the earth in order to produce the maps of the earth.  Astrophysicists analyze the light and other waves released by the distant stars and galaxies in order to deduce( realize ) information about them.

 The information conveyed in a signal may be used by humans or machines (computer or robots) for communication, forecasting, decision making etc.  The type of signal that signal processing system deals with include text, image, audio, video, ultrasonic signals etc.

NOISE :  Noise can be defined as the unwanted signals that interferes with the communication of another signals.  Noise itself is information bearing signal that conveys information regarding the source of noise. Example The noise from the engine of a car conveys information regarding the state of engine and how smooth it is running.

Application of signal processing: 1)DIGITAL WATER MARKING : Digital water marking is the embedding of a signature signal, i.e the digital watermark, underneath a host image, video or audio signal. The main challenge in water marking is to make the watermark secret imperceptible(invisible and inaudible). Watermarking is used in digital media for the following purposes.

1)Authentication of digital image and audio signals. Watermark also includes owner information, a serial number and other useful information. 2) Embedding of audio or text signals into image/video signals for retrieval. 3) Embedding a secret message into in to an image or audio signal.

BIO MEDICAL SIGNAL PROCESSING : Bio medical signal processing is concerned with The analysis, denoising and synthesis of bio Signals such as Magnetic resonance image of the brain and or electrocardiograph ( ECG) signals of the heart. An electrocardiograph signal is produced by recording the electrical voltage signals of the heart.

ECHO CANCELATION : Echo is repetition of a signal back to the transmitter either due to the coupling between the loudspeaker and microphone or due to a reflection of the transmitted signal from the points or surfaces where the characteristics of the medium through which the signals propagates changes so as to impede the propagation of the signal in the original direction such that some of the signal energy is reflected back to the source. Echo can severely affect the quality of vice conversation in telephone etc.

Modern communication system use echo cancelation system that identify the echo path and synthesis the signal and then subtract the echo signal from the original signal.

BLIND EQUALIZATION: Channel equalization is the recovery of a signal distorted in transmission through a communication channel. when the channel response is unknown the process of signal recovery is called blind equalization. USES: 1)In speech recognition for removal of the effects of the microphones and the communication channel. 2)In correction of distorted images.

SIGNAL CLASSIFICATION AND PATTERN RECOGNITION: Signal classification is used in detection, pattern recognition and decision making system. EXAMPLE: A simple binary state classifier can acts as the detector of the presence or absence of a known waveform in noise.

DETECTION OF SIGNAL IN NOISE: Signal processing is used in the detection of signal in noise. The aim is to determine if the observation consists of noise alone or if it contains a signal.

RADAR SIGNAL PROCESSING : Radar is used to estimate the range and speed of the object such as moving car or a flying aero plane. A radar system consist of a transceiver that generates and transmit signals. The signal travels with the speed of light and is reflected back from any objects in its path. The received signals are then processed to extract information of range, speed and acceleration

DIGITAL SIGNAL PROCESSING: Digital signal processing of signals involves the processing of signals by a computer or by a purpose- built signal processing microchip. The signal is stored in memory in a binary format in terms of a sequence of n bits word. To digitally process signals that are not already in a digital format, the signals need to be converted into a digital format that can be stored and processed in a computing device. Sampling and Quantization are the first two steps in all digital signal processing which have analog inputs.

ADVANTAGES OF DIGITAL FORMAT: 1)DIGITAL DEVICES Such as mobile phones all are pervasive(spreading widely through an area or a group of people ). 2)STORAGE SPACE SAVING Digital compression techniques such as mp3 can be used to compress a digital signal. 3)POWER SAVING: Power saving depends on the compression rate. Digital system can achieve power efficiency compared with analog system. 4)SECURITY: Digital system can be encrypted for security.

RECOVERY AND RESTORATION: Digital system are more responsible to recovery of lost segments. EDITING AND MIXING: Editing and mixing of audio/video and others signals in digital format is relatively easy. INTERNET AND MULTIMEDIA SYSTEM: Internet and multimedia communication would not have been possible without the digital format.

DIGITAL CODING OF AUDIO SIGNAL : Signal processing is used in the digital coding of audio signals. There are two main categories of audio coders. MODEL BASED CODERS : It is used for low bit rates speech coding in applications such as cellular telephony. TRANSFORM BASED CODERS : Used in high quality coding of speech and digital hi-fi.

HI- FI : It stands for high fidelity. Fidelity means truth, and high fidelity means staying as close as possible to the true sound of an instrument. So a record or DVD or whatever that is in hi-fi is going to sound as though you were sitting right beside the musicians. End of chapter 1